Picker for divellicating pulp

ABSTRACT

AN APPARTUS FOR DIVELLICATING SHETS INTO THEIR COMPONENT FIBERS, AND A METHOD THEREFORE, INCLUDES A CYLINDRICAL DRUM HAVING PICKING TEETH ON THE SURFACE THEREOF AND A PULP SHEET FEED GUIDE WHICH IS ADAPTED TO CONTACT THE TOP SURFACE OF THE OUTERMOST PULP SHEET SO THAT AT EACH POINT OF CONTACT BETWEEN A PLANE TANGENT TO THE TEETH TEETH THE ANGLE BETWEEN THE PLANE TANGENT TO THE TEETH AT THE POINT OF CONTACT AND THE PLANE OF THE PULP SHEET AT THE CONTACT POINT IS NOT IN EXCESS OF ABOUT 10*. THIS CAN BE ACHIEVED BY THE USE OF A FORMING GUIDE, THE INNER SURFACE OF WHICH SPIRALLY APPROACHES THE PICKING TEETH TO A POINT OF APPROXIMATELY ZERO CLERANCE, THE RADIAL DISTANCE, R, FROM ANY POINT OF THE INNER SURFACE OF THE   GUIDE TO THE CENTER AXIS OF THE DRUK BEING DETERMINED ACCORDING TO THE FOLLOWING FORMULA:   R=RO(1+KO)   WHEREIN RO IS THE RADIAL DISTANCE FROM THE INNER GUIDE SURFACE TO THE CENTER AXIS OF THE DRUM AT THE POINT OF APPROXIMATELY ZERO CLERANCE, O IS THE ANGLE IN RADIANS BETWEEN THE LINES CORRESPONDING TO RO AND THE LINE CORRESPONDING TO R, AND K IS A CONSTANT WHICH IS GREATER THAN ZERO AND LESS THAN 0.176.

Sept. 20, 1971 D, w, APPEL EIAL 3,606,175

PICKER FOR DIVELLICATING PULP.l

Filed Dec. 4. 1969 United States Patent 3,606,175 PICKER FOR DIVELLICATING PULP David W. Appel and Charles L. Sanford, Neenah, Wis.,

assignors to Kimberly-Clark Corporation, Neenah,

Wis.

Filed Dec. 4, 1969, Ser. No. 382,258 Int. Cl. B02c 4/08 U.S. Cl. 241-18 11 Claims ABSTRACT F THE DISCLOSURE An apparatus for divellicating sheets into their component fibers, and a method therefore, includes a cylindrical drum having picking teeth on the surface thereof and a pulp sheet feed guide which is adapted to contact the top surface of the outermost pulp sheet so that at each point of contact between a pulp sheet and the picker teeth the angle between the plane tangent to the teeth at the point of contact and the plane of the pulpsheet at the contact point is not in excess of about This can be achieved by the use of a forming guide, the inner surface 0f which spirally approaches the picking teeth to a point of approximately zero clearance, the radial distance, R, from any point on the inner surface of the guide to the center axis of the drum being determined according to the following formula:

wherein Ro is the radial distance from the inner guide surface to the center axis of the drum at the point of approximately zero clearance, 0 is the angle in radians between the lines corresponding to Ro and the line corresponding to R, and K is a constant which is greater than zero and less than 0.176.

DESCRIPTION OF THE INVENTION This invention relates to the air-forming of fibers and, more particularly, to a method and apparatus for divellicating pulp sheets into their component fibers.

Air-laid webs have been in use for a variety of applications for many years. The webs have been advantageously employed by themselves as absorbent pads or in other applications where low strength can be tolerated. In addition, such materials have been used in combination with base materials, such as a wide variety of nonwovens, as an applique to create a soft surface.

More recently, and as is described and claimed in the copending application of Charles E. Dunning, titled Air Formed Webs and Method for Making Such Webs, Ser. No. 882,257, filed Dec. 4, 1969, it has been discovered that useful tissue and towel products can be -made from an air laid web. Such products are characterized as possessing a desirable combination of strength, aesthetic, and absorbency properties.

For many applications, a commercially feasible process requires a method and means which is capable of divellicating pulp sheets into their component fibers at extremely high rates of production. Literally, a multitude of various picking means have been heretofore developed, but almost none of these have been capable of achieving the combination of high picking rates and good fiber separation without either causing excessive fiber breakage, scorching or burning.

Accordingly, an object of the present invention is to provide a method and apparatus for substantially completely divellicating pulp sheets into their component fibers to form air-laid webs or fluffs at substantially irnproved rates of production. A further object is to provide an economical method and apparatus of this type.

Another object lies in the provision of a Imethod and apparatus of the above-described type wherein the pulp sheets are separated into their individual fibers with only a minimum of ber breakage. A still further object is to provide a method and apparatus as hereinbefore described wherein ber separation is carried out with only a minimum of fiber scorching or burning. A more specific object of the present invention resides in providing a method and apparatus as described above wherein movement of the pulp sheets during the divellicating is achieved with a minimum amount of friction.

Other objects and advantages of the present invention will be apparent as the following description proceeds, taken in conjunction with the accompanying drawings in which:

FIG. 1 is a side elevation view partially broken away and illustrating one embodiment of the apparatus of the present invention;

FIG. 2 is a schematic view and illustrates the -manner in which a pulp sheet intersects a picker tooth; and

FIG. 3 is a schematic View and illustrating another embodiment of the apparatus of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but, on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as expressed in the appended claims.

Turning to the drawings, FIG. 1 illustrates an apparatus for divellicating pulp sheets. As shown, a series of pulp sheets 10 are forwarded to a cylindrical picker roll 12 having picker teeth 14 by the series of rolls 16, driven by means not shown. The sheets 10 are guided into contact with the picker teeth 14 by means of a pulp sheet feed guide 18 which extends around a portion of the roll; the guide beginning at point '20, ending at point 22, and passing through a point of approximately zero clearance, eg., less than 0.010 inch, with the picker teeth at the point 24.

With respect to the illustrated apparatus, it is important that, as each of the individual pulp sheets comes into Contact with the picker teeth, the plane tangent to the picker4 teeth at the point of contact intersects the plane of the pulp sheet at the contact point at an angle of less than about 10 and, preferably, less than about 5. If higher contact angles are present it is difficult to obtain complete fiber separation and fiber scorching or burning can occur.

FIG. 2 illustrates the angular relationship of the pulp sheets and picker teeth at the point of initial Contact of a sheet with the teeth. The illustrated sizes of the sheet, the picker tooth, and the picker drum are not intended to be in proportion to those employed in actual use. Also it should be understood that, in practice, the sheets spirally approach the teeth, and that the straight approach depicted is strictly for illustrating the angular relationship at the point of contact. In the figure, the line 26 lies in the plane tangent to the picker tooth 218 at the point of contact between the pulp sheet 30 and the tooth. The line 312 lies in the plane of the pulp sheet 30 at the contact point. Thus, the angle a represents the above discussed contact angle.

Referring again to FIG. 1, the angle at which the pulp sheets intersect the picker teeth is determined by the manner in which the sheets are brought into contact with the teeth by the pump feed guide 18. In order to achieve an intersecting angle of less than about 10, the radial distance, R, from any point on the inner surface of the guide, which is in contact with the outermost pulp sheet, to the center axis of the picker roll should be in accordance with the following formula:

wherein RO is the radial distance from the inner surface of the guide to the center axis, 6 is the angle in radians between the lines in the same plane corresponding to R and R0, and K is a constant which is less than 0.1761 and, preferably, less than 0.0875. More particularly, K is the tangent of the above discussed intersecting angle a. For any particular pulp sheet guide, the valve selected for K should remain substantially constant in determining the appropriate radial distance, R.

The extent to which the pulp sheet feed guide extends around the picker roll, i.e., the guide length, is, for a selected value of K, related to the thickness of the series of pulp sheets to be divellicated, or, if only one sheet is to be divellicated, the thickness thereof. The guide length should be such that, at the point where the sheets enter the guide, R is about equal to Ro plus the thickness of the series of pulp sheets. While the guide can be longer, no added advantages are obtained since it will not be effectively functioning to confine the pulp sheets and spirally guide them toward the picker teeth until that point at which R equals about R plus pulp thickness is reached.

It is desirable that the thickness of the series of pulp sheets be relatively large, eg., Is inch. Increasing thickness results in picking over a larger area of the picker roll surface since, as discussed above, the effective length of the feed guide can be greater. As picking area increases, each picker tooth has an opportunity to act on more fibers and, accordingly, more fibers can be freed from the sheets per revolution of the roll. Pulp thicknesses of a magnitude whereby the picking area is increased to an extent where picker drag on the sheets causes tensile failure should be avoided.

Desirably, in order to maximize the eficiency of the divellicating process, a soft pulp sheet is employed. Such a pulp sheet can be provided by initially forming a lowdensity sheet by employing minimal pressing or by adding chemical debonding agents or by mechanically debonding the sheet after formation. In addition, while a single, thick pulp sheet can be employed, better fiber separation results with the use of a plurality of thin sheets. For most applications, it has been found suitable to use about 3 to about 8 sheets each having a basis Weight of from about 250 to about 400 lbs/2880 ft.2 and a thickness of about 0.05() inch to about 0.125 inch.

As is well known, chemical debonding can be accomplished by including a debonding agent in the forming stage. For example, an effective soft pulp is produced by adding QCS-0.20% of Arquad 2HT quaternary amine to the pulp furnish prior to sheet formation.

yMechanical debonding can be accomplished by flexural straining of the pulp sheet such as by running the pulp sheet between mating fiuted rolls. The fiutes can be oriented either parallel to the axis of the rolls or circumferentially around the rolls or in a spiral pattern. Satisfactory results can be achieved by running narrow pulp sheets diagonally through circumferentially ribbed rolls on one diagonal and then the other. This produces components of flexural strain both in the machine direction and in the cross-machine direction resulting in a sheet that is soft and limp in all directions. Optimum debonding appears to be `obtained with the radii of the flutes being maintained between about 1/4 and 1/12 inch. The flutes should be designed to provide a constant gap at all points between the mating surfaces so that the pulp sheet is fiexed but not pressed excessively in the local areas. Since mating spiral tintes cause the pulp sheet to advance toward one end of the roll, the roll should be at an angle to the transverse direction to sheet travel.

It can be desirable in practice to employ two pairs of debonding rolls in series with opposite pitches on the iiutes so as to provide flexural straining at two angles to the machine direction of the pulp sheet.

Additionally, extensive mechanical debonding can be achieved by sharply bending the pulp sheet in a nip formed between the two rolls rotating in the same direction and employing a central wedge to assist in forcing the pulp sheet to advance into the nip at substantially the surface speed of the upper roll. The lower roll works to bend the pulp sheet on a very small radius that is commensurate with the limited space available, and subsequently aids in guiding the softened pulp sheet away from the bending area.

In accordance with a further aspect of the present invention, improved separation of the fibers can be attained by employing a relatively high density of picker teeth. Thus, it has been determined that improved separation can be accomplished by employing a picker roll having about 20 or more teeth per square inch of picker face. Such is in contrast with conventional pickers that are provided with between 2 to 12 teeth per square inch.

The height of the individual teeth is desirably maintained in a range of about 1/s to about 3/8 inch and, preferably about 1A inch. Referring again to FIG. 2, the teeth preferably have a shape such that the angle is 5-30. Teeth having such an angle, termed the rake angle, are self cleaning with respect to picked fibers and, while being quite effective in separating fibers, do not break them. The teeth may be positioned on the picker roll by employing either the conventional pin-type or the spirallywound methods.

As indicated previously, the pulp feed guide 1S illustrated in FIG. 1 spirally approaches a point of approximately zero clearance with respect to the picker teeth 14. Accordingly, it is preferred that the guide be made of a resilient material such as nylon in order to avoid wear on the picker teeth. Additionally, because friction and the like involved in confining the travel of the outermost pulp sheet along the inner surface of the guide, another aspect of the present invention provides a means for minimizing friction and the like of the guide. To this end, and as is shown in FIG. l, an air flotation or cushion between the guide and the pulp sheet is achieved by forming the pulp sheet feed guide 18 with a series of holes 34 and forcing air at a rate sufficient to form at least a molecular air cushion on the contact surface of the guide. An inner chamber 36 is formed between the guide 18 and plate 3S, the air being provided by means not shown. Desirably, the plate 38 is mounted so as to seat against the guide 18. The spring 40 provides a safety release in the event a hard object enters the picker.

Process air can be provided to the picker as is conventionally known. Thus, air from a source generally indicated at 42 is brough up into the chamber 44. The air leaves the chamber at outlet 46 and travels around the picker roll.

Further with respect to FIG. l, at the point of practically zero clearance 24, the fibers separate from the picker teeth and are directed downwardly in the form of a stream through a forming duct 48 and are deposited on the foraminous wire 54 in the form of a web 56. Suction means 5S can be provided to assist web formation.

While for the present invention, the nature of the duct 48 is not especially important, in accordance with the copending application of Appel, titled Method and Apparatus for Air Laying Pulp Fibers, Ser. No. 882,265, filed Dec. 4, 1969, webs substantially free of fiber iloccing can be obtained by appropriate positioning of the duct and using a duct of a suitable size.

As described in the above-mentioned Appel application and with reference to FIG. l herein, fiber floccing can be avoided by positioning the duct 48 such that its longitudinal axis is parallel to the plane which is tangent to the picker teeth at the port of approximately zero clearance. The width of the duct 48 is such that the process air entering the picker at 46 and the supplemental air flow 52 from the source 50 can be accommodated in the duct without a change in their velocities. Regarding the velocities of these air flows, they should be substantially equal to the velocity at which the bers leave the picker teeth at 24 which, in turn, is about the velocity of the picker teeth. As described in the Appel application, by using such an arrangement,` the fibers lmaintain an approximately constant velocity throughout their travel through the duct and, consequently, do not entangle. While the use of a supplemental air flow 52 is not essential, it is suggested that such is preferred in order to overcome fiber occulation at high picking rates. The desirability of positioning the process air entrance 46 near the forming duct entrance in order to avoid fiber clumping is also discussed in the Appel application.

FIG. 3 schematically illustrates another embodiment of the present invention which `is similar to the embodiment of FIG. l except that the forming duct is perpendicular to the forming wire. Thus, as shown, pulp sheets 60 are forwarded by rolls 62 into contact with the teeth 64 of the picker drum 66 and are confined along the path of the feed guide 68. Process air is provided from chamber 70 and the picked bers leave the picker adjacent the end of the sheet guide `68 and are formed into a moving stream. The stream of fibers is collected in the forrn of a web 712 on the moving foraminous wire 74. As was the case with the embodiment of FIG. l and in accordance with the above-identified Appel opplication, the longitudinal axis of the forming duct is parallel to the plane tangent to the picker teeth at the point of approximately zero clearance between the teeth and the guide.

Thus, as has been seen, the present invention provides a method and apparatus that is capable of achieving a high rate of picking with substantially complete fiber separation without causing excessive fiber breakage, burning or scorching. At a pulp sheet feed rate of about 80 pounds per inch of width of the picker per hour the present invention produces an air-laid web or uif which is practically free of ber clumps. Production rate of this type is on the order of about ten times the productivity obtainable on some commercially available pickers.

We claim:

1. A picking apparatus for divellicating at least one pulp sheet into its component fibers comprising a cylindrical drum having picking teeth on the surface thereof and a pulp sheet feed guide extending around a portion of the drum and approaching the drum to a point of approximately zero clearance, the inner surface of the guide being adapted to contact the top surface of the pulp sheet in such a manner as to confine the pulp sheet so that the angle formed between a plane tangent to the teeth at any point of contact with the pulp sheet and the plane of the pulp sheet at the contact point does not exceed aboct 2. The apparatus of claim 1 wherein the angle does not exceed 5.

3. A picking apparatus for divellicating a plurality of pulp sheets into their component fibers comprising a cylindrical drum having picking teeth on the surface thereof and a pulp sheet feed guide extending around a portion of the drum, the inner surface of the guide adapted to contact the top surface of the outermost pulp sheet with the inner surface of the guide spirally approaching the picking teeth to a point of approximately zero clearance, the radial distance, R, from any point on the inner surface of the guide to the center axis of the drum `being determined according to the following formula:

R=R0(1+K0) wherein Ro is the radial distance from the inner guide `surface to the center axis of the drum at the point of' approximately zero clearance, 0 is the angle in radians between the line corresponding to Ro and the line corresponding to R, K is a constant which is greater than zero and less than 0.176.

4. The apparatus of claim 3 wherein K does not exceed 0.0875.

5. The picking apparatus of claim 4 and including means for decreasing the frictional contact between the inner surface of the guide and the top surface of the outermost pulp sheet.

6. The picking apparatus of claim 5 wherein the means for decreasing the frictional contact includes a iluid chamber, means for supplying fluid to the chamber and the guide includes a series of aperture means allowing the fluid to pass through the guide to contact the top surface of the outermost pulp sheet.

7. The picking apparatus of claim 4 wherein the picking teeth have a height of up to about 1A inch and are located on the drum at a frequency of at least 20 per square inch.

8. A method of divellicating a plurality of pulp sheets into their component fibers which comprises providing a rotating cylindrical drum having picking teeth on the surface thereof, bringing the pulp sheets into contact with the picker teeth and confining the pulp sheets in a path around a portion of the drum so that the top surface of the outermost pulp sheets spirally approaches the picking teeth to a point of approximately zero clearance, the radial distance, R, from any point on the top surface of the outermost pulp sheet to the center axis of the drum being determined according to the following formula:

wherein Ro is the radial distance from the top surface of the outermost pulp sheet to the center axis of the drum at the point of approximately zero clearance, 0 is the angle in radians between the line corresponding to RU and the line corresponding to R, and K is a constant which is greater than zero and less than 0.176.

9. The process of claim 8 wherein K is less than 0.0875.

10. A method of divellicating at least one pulp sheet into `its component fibers which comprises providing a rotating cylindrical drum having picking teeth on the surface thereof, bringing the pulp sheet into contact with the picker teeth, confining the pulp sheet in a path around a portion of the drum so that the angle formed between a plane tangent to the teeth at any point of contact with the pulp sheet and the plane of the pulp sheet at the contact point does not exceed about 10 and transporting the picked bers away from the teeth.

11. The method of claim 10 wherein the angle does not exceed 50.

References Cited UNITED STATES PATENTS 663,868 12/1900 Cream 241--18X 2,890,493 6/ 1959 Clark 24l-47X 3,491,956 1/1970 Campman et al. 241-57 3,519,211 7/1970 Sakulich et al 241-18 r GRANVILLE Y. CUSTER, JR., Primary Examiner U.S. Cl. X.R. 241-47 gg UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3, 606, 175 Dated September 2 0, 1971 Inventods) David W. Appel and Charles L. Sanford It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

'- In the specification at Column 3, line 13, "valve" should read Value In claim 11, line 2, H50"" Should read 5 Signed and sealed this 15th day of April 1972.

(SEAL) Attest:

ROBERT GOTTSCHALK EDWARD M.FLETCHER,JR.

Commissioner of Patents Attestng, Officer 

